Field of the Invention
This invention relates to systems and methods for producing scaffolds and, more particularly, to systems and methods for producing scaffolds having desired physical properties.
Description of the Prior Art
Tissue engineering and regenerative medicine have the potential to develop novel biosynthetic materials for improved treatment, maintenance, and regeneration of diseased or damaged tissue. Development and design of materials that utilize tissue engineering strategies to mimic the functionality of native tissue requires consideration of cell type, seeding and attachment, molecular signals, and macromolecular matrix. See Sands R W, Mooney D J. Polymers to direct cell fate by controlling the microenvironment. Curr Opin Biotechnol 2007 October; 18(5):448-453; Freed L E, Vunjak-Novakovic G, Biron R J, Eagles D B, Lesnoy D C, Barlow S K, et al. Biodegradable Polymer Scaffolds for Tissue Engineering. Bio/Technology 1994; 12(7):689-693; Venugopal J, Low S, Choon A T, Ramakrishna S. Interaction of cells and nanofiber scaffolds in tissue engineering. J Biomed Mater Res B Appl Biomater 2008 January; 84(1):34-48.
Many types of engineered tissue rely on a provisional or permanent scaffold to generate a three-dimensional framework for cell attachment and tissue organization. Both natural and synthetic scaffold materials are used in tissue engineering. See Ott H, Matthiesen T, Goh S, Black L, Kren S, Netoff T, et al. Perfusion-decellularized matrix: using nature's platform to engineer a bioartificial heart. Nature Medicine 2008; 14(2):213-221; Courtney T, Sacks M S, Stankus J, Guan J, Wagner W R. Design and analysis of tissue engineering scaffolds that mimic soft tissue mechanical anisotropy. Biomaterials 2006 July; 27(19):3631-3638. Synthetically derived cell scaffolds can be permanent or degradable and facilitate expression and organization of the extracellular matrix (ECM). Architectural cues in these scaffolds have been shown to affect the morphology, organization, and phenotypic expression of cells in vitro. See Engelmayr G C, Jr., Cheng M, Bettinger C J, Borenstein J T, Langer R, Freed L E. Accordion-like honeycombs for tissue engineering of cardiac anisotropy. Nat Mater 2008 December; 7(12):1003-1010; Fromstein J D, Zandstra P W, Alperin C, Rockwood D, Rabolt J F, Woodhouse K A. Seeding bioreactor-produced embryonic stem cell-derived cardiomyocytes on different porous, degradable, polyurethane scaffolds reveals the effect of scaffold architecture on cell morphology. Tissue Eng Part A 2008 March; 14(3):369-378; Guido S, Tranquillo R T. A methodology for the systematic and quantitative study of cell contact guidance in oriented collagen gels: Correlation of fibroblast orientation and gel birefringence. J Cell Sci 1993 June; 105 (Pt 2):317-331. In order to develop effective implants, tissue engineers need to be able to specify and tune the scaffold's morphological features for different applications. In addition, scaffold architecture must be designed to provide cues for cellular organization and form the basis for engineered tissue constructs that mimic tissue-specific organization and physical properties.
Cardiac tissue is an example of highly structured tissue that relies on cellular organization for its function. See Simpson D, Terracio L, Terracio M, Price R, Turner D, Borg T. Modulation of cardiac myocyte phenotype in vitro by the composition and orientation of the extracellular matrix. J Cell Physiol 1994; 161(1); Goldsmith E C, Hoffman A, Morales M O, Potts J D, Price R L, McFadden A, et al. Organization of fibroblasts in the heart. Dev Dyn 2004; 230(4). Cell scaffold materials can help cardiac tissue development by: (1) providing cues that induce alignment of cardiac myocytes; (2) allowing sufficient nutrient and cell infiltration necessary for forming a three-dimensional tissue construct; (3) modulating the cell type distribution of co-cultures; and (4) mimicking anisotropic mechanical stiffness of the heart. Scaffolds used for cardiac tissue engineering applications require development of design specifications for scaffold alignment, structure, porosity, and stiffness, all of which will influence cellular development, overall tissue organization, and bioreactor integration. See Eschenhagen T, Zimmermann W H. Engineering myocardial tissue. Circ Res 2005; 97(12):1220-1231; Charles-Harris M, del Valle S, Hentges E, Bleuet P, Lacroix D, Planell J A. Mechanical and structural characterisation of completely degradable polylactic acid/calcium phosphate glass scaffolds. Biomaterials 2007 October; 28(30):4429-4438; Radisic M, Park H, Gerecht S, Cannizzaro C, Langer R, Vunjak-Novakovic G. Biomimetic approach to cardiac tissue engineering. Philos Trans R Soc Lond B Biol Sci 2007; 362(1484):1357.
Various methods have been employed to fabricate scaffolds of varying porosities and anisotropies. For example, microfabrication techniques have been used to fabricate scaffolds with aligned structures. See Huang N F, Patel S, Thakar R G, Wu J, Hsiao B S, Chu B, et al. Myotube assembly on nanofibrous and micropatterned polymers. Nano Lett 2006 March; 6(3):537-542; Norman J J, Desai T A. Control of cellular organization in three dimensions using a microfabricated polydimethylsiloxane-collagen composite tissue scaffold. Tissue Eng 2005; 11(3-4):378-386. Electrospinning methods have been employed with post-process elongation to produce anisotropic fibrous scaffold architecture. Zong X, Bien H, Chung C Y, Yin L, Fang D, Hsiao B S, et al. Electrospun fine-textured scaffolds for heart tissue constructs. Biomaterials 2005 September; 26(26):5330-5338. In order to create scaffolds that allow adequate nutrient and oxygen diffusion, methods such as three-dimensional fiber deposition, sacrificial fiber electrospinning, and phase separation have been utilized to generate scaffolds of controlled porosities. See Hollister S J. Porous scaffold design for tissue engineering. Nat Mater 2005 July; 4(7):518-524; Baker B M, Gee A O, Metter R B, Nathan A S, Marklein R A, Burdick J A, et al. The potential to improve cell infiltration in composite fiber-aligned electrospun scaffolds by the selective removal of sacrificial fibers. Biomaterials 2008 May; 29(15):2348-2358; Khorasani M T, Shorgashti S. Fabrication of microporous polyurethane by spray phase inversion method as small diameter vascular grafts material. J Biomed Mater Res A 2006 May; 77(2):253-260; Moroni L, de Wijn J R, van Blitterswijk C A. 3D fiber-deposited scaffolds for tissue engineering: influence of pores geometry and architecture on dynamic mechanical properties. Biomaterials 2006 March; 27(7):974-985. Spray phase separation (SPS) is method for creating scaffolds that permits control over alignment, porosity, and stiffness; however this method has not been directly applied for cardiac tissue scaffolds. See Khorasani M T, Shorgashti S. Fabrication of microporous polyurethane by spray phase inversion method as small diameter vascular grafts material. J Biomed Mater Res A 2006 May; 77(2):253-260.
SPS-fabricated scaffolds are produced using a method that sprays a polymer solution onto a surface while simultaneously spraying a nonsolvent onto the surface. The nonsolvent mixes with the solvent and the polymer causing the polymer to precipitate. Some groups have used SPS methods to fabricate materials of varying porosity for drug delivery devices and vascular graft materials. See Kreitz M R, Webber W L, Galletti P M, Mathiowitz E. Controlled delivery of therapeutics from microporous membranes. I. Fabrication and characterization of microporous polyurethane membranes containing polymeric microspheres. Biomaterials 1997 April; 18(8):597-603; Khorasani M T, Shorgashti S. Fabrication of microporous polyurethane by spray phase inversion method as small diameter vascular grafts material. J Biomed Mater Res A 2006 May; 77(2):253-260; Okoshi T, Chen H, Soldani G, Galletti P M, Goddard M. Microporous small diameter PVDF-TrFE vascular grafts fabricated by a spray phase inversion technique. ASAIO J 1992 July-September; 38(3):M201-206. SPS fabrication methods can be used to vary scaffold properties such as alignment, porosity, stiffness, and anisotropy, which are key features for directing cellular development, overall tissue organization, and bioreactor integration. See Eschenhagen T, Zimmermann W H. Engineering myocardial tissue. Circ Res 2005; 97(12):1220-1231; Charles-Harris M, del Valle S, Hentges E, Bleuet P, Lacroix D, Planell J A. Mechanical and structural characterisation of completely degradable polylactic acid/calcium phosphate glass scaffolds. Biomaterials 2007 October; 28(30):4429-4438; Radisic M, Park H, Gerecht S, Cannizzaro C, Langer R, Vunjak-Novakovic G. Biomimetic approach to cardiac tissue engineering. Philos Trans R Soc Lond B Biol Sci 2007; 362(1484):1357.
Accordingly, there is a need in the pertinent art for systems and methods of efficiently producing scaffolds having selectively adjustable mechanical properties. In particular, there is a need in the pertinent art for systems and methods of efficiently and accurately producing scaffolds having selected structural alignment, porosity, and stiffness. There is a further need in the pertinent art for systems and methods for producing composites formed from multiple scaffolds.